In the construction of water cooled internal combustion engines, it is common practice to cast the cylinder block and its water jacket in one piece and to provide in the walls of the water jacket suitable apertures to permit the removal of the sand at the termination of the casting operation. When the engines are finally assembled, these openings are then closed with suitable dished plates or plugs. Advantage has been taken of the presence of these apertures in the water jacket by removing one of those plugs and mounting an electric heating device in place thereof. In general, these electrical heating devices take the form of a disc shaped body member with a heating element that extends within the water jacket and has terminals accessible at the outside of the disc, with the terminals being connected to a suitable energy source for the purpose of energizing the heater to keep the engine temperature heated to an acceptable level during cold weather.
A variety of so-called frost plug heaters are known in the art. A representative, although not exhaustive, list of these devices in the patent literature include:
______________________________________ U.S. Pat. No. Inventor Issue Date ______________________________________ 2,401,847 Urbant et al 06/11/46 2,783,352 McKay 02/26/57 2,824,945 Derumaux 02/25/58 3,143,634 Windsor 08/04/64 3,148,268 Heinbuch 09/08/64 3,157,773 Pickard 11/17/64 3,165,621 Windsor 01/12/65 3,209,123 Windsor 09/28/65 3,211,888 Windsor 10/12/65 3,229,069 Kerl et al 01/11/66 3,280,298 Klancke et al 10/18/66 3,456,094 Klancke et al 07/l5/69 3,587,548 Wernicke 06/28/71 3,646,314 Windsor 02/29/72 4,175,229 Brinkhof et al 11/20/79 4,242,564 Kendall 12/30/80 4,465,039 Snelgrove et al 08/14/84 4,480,604 Chang et al 11/06/84 4,485,771 Brinkhof et al 12/04/84 Canadian 512,017 Beaton et al 04/19/55 Canadian 850,767 Ehgoetz 09/01/70 ______________________________________
Insofar as the present invention is concerned, it is believed that U.S. Pat. No. 3,646,314; U.S. Pat. No. 4,175,229; and Canadian Pat. No. 850,767 are the most pertinent. Each of the constructions shown in these patents have their various drawbacks. For example, the construction shown in the '314 patent is designed with the head of the screw on the interior side of the disc. As a result, much of the screw extends outwardly when the device is in place. Consequently, a low profile of the device is not obtainable, since the screw juts out a considerable distance from the disc. This has certain disadvantages not only from an aesthetic viewpoint but also in manufacturing. For example, this design is somewhat cumbersome to install especially in an automated assembly line. Since the screwhead is on the inside in this prior approach, it is not possible to be engaged by an automated tool to turn the screw and thus tighten the assembly.
The Canadian '767 patent has drawbacks because this approach generally requires that the disc have a very thin wall, typically on the order of 1/16 inch thick or less. If a much thicker disc is used then there is not a sufficient amount of tilt allowed to permit the clamping member to enter through the bore in the engine block. The use of such a thin walled disc is disadvantageous by the inability to provide a rugged device construction with cost effective materials and manufacturing processes. It will also be noted that in this prior art approach that an oversized aperture is provided through which the screw extends and that the screw is threaded right into the clamping member. Thus, in order to get the clamping member through the bore in the engine block it is necessary to cant the screw a considerable distance. Since the aperture in the disc is relatively large, the chances of leakage are increased.
The '229 U.S. patent discloses a relatively complex structure in that it relies upon two separate wing shaped clamping members, a spring, and a nut design which may become disengaged from the screw. As a result, this approach tends to be relatively costly to manufacture from both a materials and labor standpoint.